1. Field of the Invention
The present invention relates to a liquid crystal display (LCD) device and a method for fabricating the same, and more particularly, to an LCD device having an enhanced displaying quality of screen in a structure of minimizing a damage of a column spacer due to vibration caused by an external force, and a method for fabricating the same.
2. Background of the Invention
Generally, a liquid crystal display (LCD) device is being widely used due to advantages such as a light weight, a thin thickness, and low power consumption. Accordingly, the LCD device is being widely used to display images on screens of a portable computer, a portable phone, and office automation equipment.
The LCD device displays desired images on a screen by controlling optical transmittance according to image signals applied to a plurality of controlling switching devices arranged in a matrix format.
The LCD device comprises an upper substrate as a color filter substrate, a lower substrate as a thin film transistor (TFT) array substrate facing the upper substrate, an LC panel including an LC layer sandwiched by the upper and lower substrates, and a driving portion for driving the LC panel by supplying scan signals and image information to the LC panel.
FIG. 1 shows a cross-sectional view of a LCD device according to the related art. As shown in FIG. 1, a general LCD device according to the related art includes a first substrate 1a defining a thin film transistor (TFT) substrate, a second substrate 1b defining a color filter substrate, and an LCD layer 40 interposed between the first substrate 1a and the second substrate 1b. 
Although not shown in detail in the drawing, gate lines 2 and data lines (not shown) which cross each other horizontally and perpendicularly on the first substrate 1a to define a plurality of pixels, and a TFT 4 is disposed at each crossing between the gate line 2 and the data line of each pixel.
The TFT 4 includes a gate electrode 4a formed on the first substrate 1a, a gate insulating layer 4b on the gate electrode 4a, an active layer 4c on the gate insulating layer 4b, and source electrode 4d and drain electrode 4e both on the active layer 4c. The source electrode 4d and the drain electrode 4e are covered with a protection film 9.
A plurality of protrusions 8 having a double-layered structure are formed on each gate line 2 on the first substrate 1a. Each protrusion 8 is implemented, having a layer 8a formed on the same layer as the active layer 4c being located and made of the same material as the active layer 4c, and a layer 8b formed on the same layer as the source and drain electrodes 4d and 4e being located and made of the same material as those electrodes 4d and 4e. 
Referring to FIG. 1, a column spacer 7 for maintaining a gap (space) between the first substrate 1a and the second substrate 1b is formed on the second substrate 1b. The column spacer 7 is partially overlapped with the protrusion 8 formed on the first substrate 1a. 
If it is assumed that part of the column spacer 7 overlapped with the protrusion 8 is referred to as a first column spacer 7a and part of the column spacer 7 not overlapped with the protrusion 8 is referred to as a second column spacer 7b, the first column spacer 7a serves to maintain a constant gap between the first substrate 1a and the second substrate 1b together with the protrusion 8, and the second column spacer 7b is configured to come in contact with a top layer of the first substrate 1a when the second substrate 1b is pressed by a user's touch or the like, so as to prevent the deformation of the first and second substrates 1a and 1b and induce a fast restoration thereof.
Although not shown in detail, the first and second substrates 1a and 1b are received and fixed in a casing including a lower cover (not shown), an upper cover (not shown) and a main support (not shown) and the like. Most of such casing is disposed to press edges of the first and second substrates 1a and 1b. 
The general LCD device according to the related art having such configuration is configured such that the first column spacer 7a and the protrusion 8 are not bonded to each other but rather contacted by each other directly or indirectly. Accordingly, the first column spacer 7a and the protrusion 8 may move in respectively different directions due to vibration caused by an external force, resulting in friction occurred therebetween. In this case, the first column spacer 7a may partially be deformed or damaged, which may cause the change in the gap between the first substrate 1a and the second substrate 1b. The deformation or damage of the first column spacer 7a due to such friction results from the first column spacer 7a having a greater size than the protrusion 8 and being made of polymer with elasticity.
In particular, the deformation or damage of the first column spacer 7a frequently occurs at an area adjacent to the casing. This is because in case where a vibration caused by an external force is applied to the first and second substrates 1a and 1b, while the protrusion 8 defined at the area adjacent to the casing moves in a certain direction, the first column spacer 7a generates resistance in a direction opposite to the movement direction of the protrusion due to an interference of the case.
FIG. 2 is a photograph showing an image defective area in the related art LCD device of FIG. 1. Referring to FIG. 2, if the gap between the first substrate 1a and the second substrate 1b is changed due to the deformation or damage of part of the first column spacer 7a formed at the area adjacent to the casing, an image defective area may be generated at areas corresponding to edges of the first and second substrates 1a and 1b. Moreover, as the LCD device is used for longer time, the image defective area is expected to be increased.